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hCG
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Common Questions
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1. How does the test that I do at home myself compare with the results of a test done in a lab?
2. What is an ectopic pregnancy?
3. When is a blood hCG test ordered instead of a urine hCG?
4. How many days after a miscarriage would it take for a urine pregnancy test to show a negative result?
1. How does the test that I do at home myself compare with the results of a test done in a lab?
Home pregnancy testing is very similar to qualitative urine hCG testing in the laboratory, but there are factors surrounding its use that are important to note.
- First, home tests come with very specific directions that must be followed explicitly. If you are using a home test, follow the directions extremely carefully.
- Second, home tests are sometimes done too soon after the missed menstrual cycle to result in a positive test; it takes 10 days after conception before the presence of hCG can be detected by the urine test. That is why a home test is sometimes negative when the test done by your doctor is positive—the doctor’s test is often done several days later when hCG levels have become detectable.
- All urine qualititative hCG tests should be done on a first morning urine sample, if possible. Urine becomes more dilute after ingestion of liquids (coffee, juice, water, etc.) and urine hCG concentrations may become too low to register as positive.
Generally, when used correctly, the home test should produce the same result as the urine hCG test done by your doctor. Qualitative blood testing for hCG may be more sensitive than urine hCG testing, so sometimes a blood test will indicate pregnancy when the urine test is negative. Quantitative hCG testing requires a blood sample and must be done in the laboratory.
2. What is an ectopic pregnancy?
An ectopic pregnancy is the condition when the fertilized ovum (blastocyst) implants somewhere other than in the uterus. This is a serious condition needing immediate treatment. Patients with ectopic pregnancies often have abdominal pain and uterine bleeding. Usually, abnormally low levels of hCG are produced in ectopic pregnancies with slower-than-normal rates of increase.
3. When is a blood hCG test ordered instead of a urine hCG?
The blood hCG test actually measures the amount of hCG in the blood; the urine hCG is used to detect the presence of hCG. Since hCG is not normally detected in the urine of a non-pregnant woman, the urine hCG is enough to confirm a pregnancy. Sometimes, it is important to know how much hCG is present to evaluate a suspected ectopic pregnancy or to monitor a woman following a miscarriage. In these circumstances, your doctor will run a blood hCG.
4. How many days after a miscarriage would it take for a urine pregnancy test to show a negative result?
Urine hCG disappears at about the same rate as serum hCG, which can take anywhere from 9 to 35 days, with a median of 19 days. However, the timeframe for when an hCG result will be negative is dependent on what the hCG level was at the time of the miscarriage. Frequently, miscarriages are monitored with quantitative blood hCG testing. If the levels of hCG do not fall to undetectable levels, some hCG-producing tissue may remain and have to be removed.
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This article was last reviewed on
February 9, 2008.
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